Method for modifying the design of a structural part

ABSTRACT

A method for modifying the design of a component with regard to one or more criteria using a virtual model of the component, wherein a virtual model of the component is produced by combination of the component from basic objects with the aid of Boolean operators, and each basic object is assigned an information element in which attributes of the basic object are stored. Each basic object is decomposed into primitive objects which are combined with aid of Boolean operators, the primitive objects being surfaces or bodies which can be decomposed into rasters. Each geometrical contact surface is assigned a connecting element in which information for coordinating the objects is stored, and the rastering of the primitive objects is performed by a conventional gridding method. A modification of the geometrical shape of objects is undertaken with the information elements defining the limits of possible modifications.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of Application No. 100 43 737.0,filed Sep. 5, 2000 in Germany, and PCT DE01/03350, filed on Sep. 4,2001.

The invention relates to a method for modifying, in particular foroptimizing, the design of a component with regard to one or morecriteria using a virtual model of the component.

The current development processes are developing from stepwisedevelopment towards simultaneous development, the disciplines oftechnical development and analysis being in closer cooperation, andknowledge of all relevant technical disciplines being introduced inearly phases of product development. Simultaneous development is foundto be necessary in order to develop products with improved technologyand of higher quality in a shorter development time, something whichalso leads to reduced costs.

The probability of the development of better and less expensivecomponents is rising in principle through the application of highperformance analysis tools and the knowledge of experts in the variousfields of engineering science. A possible impediment to success is,however, the normally limited time in which the components have to bedeveloped.

With this in mind, the multidisciplinary design optimization (MDO) isregarded as an effective method for improving quality and performance ofproducts in conjunction with reducing costs. This happens chieflythrough shortening the evaluation time required overall for a designcycle, and by creating an automated analysis tool which searches for thebest solution or performs specific tasks in a limited time.

Various publications provide a good overview of the state of the art inmultidisciplinary design optimization. To name only a few, there are thearticles by Alexandrov edit. [Natalia Alexandrov and M. Y. Hussaini,editors, Multidisciplinary Design Optimization—State of the Art, SIAM1997], Bartholomew [Peter Bartholomew, The role of MDO within aerospacedesign and progress towards an MDO capability; in 7thAIAA/USA/NASA/ISSIMO Symposium on Multidisciplinary Analysis andOptimization, p. 2157-2165; AIAA, 1998], Kroo [Ilan Kroo; Mdo forlarge-scale design; in Natalia M. Aleandrov and M. Y. Hussaini, editors,Multidisciplinary Design Optimization—State of the Art, pages 22-44;SIAM, 1997], Sobieski and Haftka [Jaroslaw Sobieszczanski-Sobieski andRaphael T. Haftka; Multidisciplinary aerospace design optimization:Survey of recent developments, Conference Paper 96-0711, AIAA, 1996.Presented at the 34th Aerospace Sciences Meeting and Exhibit; Jan.15-18, 1996] and Vanderplaats [G. N. Vanderplaats; Structural designoptimization status and direction; Journal of Aircraft, 36(1):11-20,January-February 1999].

Sobieski and Haftka distinguish between three categories ofmultidisciplinary design optimization, which place differentrequirements on EDP and organization.

-   -   The first category comprises only a few technical disciplines.        An expert can process all the required information and all        necessary knowledge.    -   The second category comprises all methods which achieve the        multidisciplinary object, all the required technical disciplines        being introduced at a low degree of complexity. This        optimization method is mostly applied to the design concept of a        system, the analysis tools being used as individual modules. If        these methods are, applied to tasks in the continuing design        process, they are confronted with some of the organizational        challenges set by multidisciplinary design optimization.    -   The third category is described as a stage of the challenge in        terms of computing and organization. In order to permit the        analysis in a modular environment, specific techniques, for        example, decomposition, approximation and comprehensive sensor        technologies are used as tools in order to organize the modules        themselves and the exchange of data.

Similar classifications are proposed in other publications, for exampleby Bartholomew and Kroo. They distinguish between the various degrees ofcomplexity and accuracy of the applied analysis programs and theoptimization architecture.

The publications described above lead to a modular analysis environment,something which necessitates the use of decomposition and approximationtechniques in order to be able to solve relatively complex design tasks.Kroo explains the necessity to develop the parameterized geometry atdifferent degrees of detail and abstraction in order to be able to applythe multidisciplinary optimization to realistic, large-scale designtasks which comprise many disciplines and analysis tools from the stateof the art.

In order to permit the fully automated design optimization with the useof a parameterized geometry at different degrees of detail, the geometrymodelling must be more strongly linked to the rastering. Samareh[Jamshid A. Samareh; Status and future of geometry modelling and gridgeneration for design and optimization; Journal of Aircraft,36(1):97-104, January-February 1999] compiles an overview of therequirements to be fulfilled and the problems to be solved in order tocreate such a fully automated geometry model and a rastering method formultidisciplinary optimization applications.

Another aspect of multidisciplinary design optimization is discussed byWood and Bauer in [Richard M. Wood and Steven X. S. Bauer; A discussionof knowledge based design; Conference Paper 98-4944, AIAA, 1998;Presented at the 7th AIAA/USAF/NASA/ISSMO Symposium on MultidisciplinaryAnalysis and Optimization; Sep. 2-4, 1998]. Wood and Bauer point out theneed to allow expert knowledge to flow into the optimization process inorder to improve the technology and quality of the products. They saythat knowledge from previous design cycles must flow into the earlyphase of the design process.

None of the solutions known from the prior art permits a completelyautomated design optimization.

It is an object of the present invention to propose a completelyautomated method for multidisciplinary design optimization of the two-,quasi- three- or three-dimensional component which permits small-scalechanges to be transferred to the complete component.

The inventive method can be used to modify a component, in particular tooptimize it, by applying modifications to different stages of details ofthe component. The first stage is to create a virtual model of thecomponent. For this purpose, the component is combined from basicobjects with the aid of solid modelling Boolean operators, the basicobjects being, in particular, surfaces or rotationally symmetricalbodies. Each of the basic objects is assigned an information element inwhich the attributes of the respective basic object, in particularparameter values, interval limits and rules, are stored. Theseattributes determine and delimit the respective basic object.

It has hereby become possible to render accessible to multidisciplinarydesign optimization geometries and/or basic objects to which knowledgeand/or information is allocated.

Each basic object is then constructed from further basic objects or oneor more primitive objects which are combined with the aid of Booleanoperators. The primitive objects are surfaces or bodies of differentcomplexity and geometrical multiplicity which can be decomposed intorasters. Each further basic object or primitive object can again beassigned an information element in which the attributes of the furtherbasic object or the primitive object, in particular parameter values,interval limits and rules, can be stored. These attributes determine anddelimit the respective primitive object.

The Boolean combination of the component from individual basic objectsyields geometrical contact surfaces or contact lines between two or moreobjects. The same also holds for the primitive objects. Each of thesegeometrical contact surfaces and contact lines is assigned a connectingelement in which information for coordinating the objects is stored.

These so-called connecting or coordination elements can also beallocated as additional knowledge to each basic object or primitiveobject in order to obtain a better subdivision into rasterable surfacesin the further process.

The primitive objects are rastered in the next step, specifically by aconventional griding method.

The modification of the component can be undertaken subsequently. Thisis performed by modifying individual or a group of objects, theinformation of the information elements defining the limits of possiblemodifications, the connecting elements defining the coordination of theobjects. Customary raster techniques are applied in this case.

The proposed model is a feature-based geometry model which permitsmultidisciplinary optimization in different degrees of detail. It usesan object-oriented access in order to produce the geometry and tointegrate all the information required during the design process. Thegeometry at different degrees of detail permits starting with atwo-dimensional geometry, then with rotationally symmetrical orstretched bodies, and finally with a realistic, three dimensionalgeometry.

The basic objects can be constructed from one or more further basicobjects or primitive objects which can be combined by Boolean operators.Each basic object is again assigned an information element in this case,in which attributes of the basic object, in particular parameter values,interval limits and rules, are stored. Each geometrical contact surfaceor contact line which is produced in the case of the Boolean operationbetween two or more objects is assigned a connecting element in whichinformation for coordinating the objects is stored.

The primitive objects can also be constructed from one or more furtherprimitive objects, as a result of which it is possible to modify thedegree of detail or the degree of construction of the model can bemodified.

The primitive objects can, in turn, be combined by Boolean operators.They can be assigned in each case an information element in whichattributes of the primitive object, in particular parameter values,interval limits and rules, are stored. Each geometrical contact surfaceor contact line which is produced in the case of the Boolean operationbetween two or more objects can be assigned a connecting element inwhich information for coordinating the objects is stored.

The modification of the geometrical shape is preferably performedexclusively or predominantly on the lowest object plane, that is to saythe primitive objects, it being possible to raster the objects to bemodified.

The inventive method proposed permits the multidisciplinary optimizationof a component by modifying the degree of detail. Each technicaldiscipline can start with the optimization at the stage optimum for it.The details of this design can be changed during the optimizationprocess without the need for a complete change to the structure andtopology of the previously designed geometry.

All the information required in later design steps can be taken from theinformation elements assigned to the individual objects, or be derivedfrom the information. The information contained can be employed orpassed to other tools.

The inventive modification method is preferably applied to optimize acomponent. It is preferably used after termination of the basicconception with a lower level of detail, and increases the variety ofdetail and the complexity of the topology as the process progresses.

The degree of the level of detail of the geometry of the model can bemodified by changing the type of the primitive objects, by addingfurther objects to the preceding model, that is to say the latter isconstructed from further basic objects and/or primitive objects.

A feature of the component can be represented by combining a primitiveobject with an information element which contains attributes of theobject. These can be, in particular, parameter values, interval limitsor rules. The rules reflect the knowledge of a person skilled in the artof the respective fields. It is thus therefore possible to define afeature of the component as a geometrical object which contains all thespecific information which is required to determine and to delimit thegeometry.

It is also possible to derive from the information stored in theinformation element further information and rules which are required inlater design phases.

In order to render automated geometry modelling and rastering possible,it is desirable to maintain the principle features of each primitiveobject during the assembly of the topology of the overall component. Themodelling technique is expanded for this purpose by creating additionalcurves or surfaces at the points at which objects are connected to oneanother or separated from one another.

These additional curves or surfaces are termed connecting elements. Theconnecting elements are used in order to decompose the geometry, whichis constructed from rasterable constituents, into these rasterableconstituents. These elements can both be produced automatically duringthe modelling with the aid of Boolean operators, and be allocated toeach object as additional knowledge. It is then easy to produce a rasterfor the rasterable primitive objects.

Boolean operators produce an object which includes two or more primitiveobjects and one or more connecting elements between the primitiveobjects. Which type of object is selected for the primitive objectdepends on the degree of detail. With each further combination ofobjects, the degree of assembly and thus the degree of detail isincreased.

Each connecting element includes curves or surfaces which cut theprimitive objects such that they do not overlap, but meet preciselyalong this curve or surface. By using this technique, the topology ofeach primitive object can remain substantially the same during theoptimization process. The production of the connecting elementscorresponds to the customary raster methods, in which specificconnecting conditions are determined for each object.

In another version of the inventive method, the Boolean operations arecombined with an optional generation of intersection sets ofneighbouring objects which are introduced into the connecting element.These intersection sets are created where the two objects intersect. Theconnecting elements then contain information on possible connectingsurfaces or connecting lines between neighbouring objects. Theconnecting elements can then be positioned for the rastering such thatthey obey as well as possible the rules for producing rasters.

The primitive objects are preferably standardized, rasterable parts suchas triangles, rectangles, pentagons, tetrahedra, pentahedra orhexahedra.

The primitive objects are preferably produced from surfaces or bodieswhich use lower geometrical objects, and which are combined with the aidof Boolean operators or by rotation, stitching or stretching. Primitiveobjects of the lowest degree of detail are objects such as circular orrectangular surfaces or bodies. The degree of detail grows through theuse of objects such as B-spline curves or B-spline surfaces in order todescribe the contours or surfaces. The degree of detail is characterizedby the degree of the geometrical variety. If the number of theparameters rises, the objects become more general and the variety ofgeometrical shapes rises.

The resulting primitive objects are preferably standardized. They havethe same input and output parameters, in order to permit a simpleexchange between primitive objects of different degrees of detail.

An automated rastering is rendered possible by the assembly ofrasterable primitive objects and the insertion of the connectingelements. The production of the connecting elements falls back onknowledge from the decomposition of geometry using the finite elementmethod.

The actual rastering by a commercially available raster generator can bepreceded by a preparatory step which makes available the data which arerequired by the raster generator.

Geometrical information such as, for example vertices, corners,surfaces, bodies, and specific raster information such as, for example,the number of elements, the type of the elements, the number of nodes,can be made available in the preparatory step. The entire geometry isdecomposed at the connecting elements in the case of the method ofrastering preferably used.

The result is individual surfaces for the production of atwo-dimensional raster, or individual bodies for the production of athree-dimensional raster.

The advantage of the joining of geometrical modelling and rastering inone system is the high degree of accuracy in the geometry, which is thentransferred to a commercially available raster generator. Processes suchas the connection of edges which adjoin one another at their end points,the filtering out of corners which are shorter than a prescribedtolerance, or the closing of gaps between edges, can be carried out byusing the information from the geometrical model.

Boolean operations which are applied during the production of thegeometrical model can cause a change in the contours of the originalprimitive objects. The contour edges can be shortened, or new edges canbe added. The recognition of which edges can be connected is therebyimplemented. Both the raster surface or the raster body, and the edgesof surfaces which belong to the sides of an element can be filtered outby means of this recognition.

In addition to this recognition process, it is possible to carry outother operations such as, for example, filtering and closing edges. Allthe information used for commercial raster generation can be derivedfrom the objects recognized.

Additional information which is relevant for the production of rasterscan be input in to the module or determined during the rasterproduction.

The production of connecting curves between two objects is explained inmore detail below with the aid of FIGS. 1 to 3:

FIGS. 1 to 3 show the production of connecting curves for surfaces. Themethod is the same for bodies, except that curves are used instead ofpoints, and surfaces are used instead of curves in order to produce theconnecting surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the production of a connecting curve between two surfaces;

FIG. 2 shows a connecting curve between verticles or corners of the bodyif a body is entirely extracted from another body;

FIG. 3 shows a connecting curve developed between the two contours atthe point with a minimum distance between opposite corners or surfaceswhen a body is entirely extracted from another body;

FIG. 4A shows a first method parameterizing contours;

FIG. 4B shows a second method of parameterizing contours;

FIG. 5 shows an example of a decomposition of a turbine wheel;

FIGS. 6A-6D illustrate the geometry of a rotor disc; and

FIGS. 7A-7B show a finite raster produced for a rotor disc.

DETAILED DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below with the aid of aturbine wheel and with reference to FIGS. 4 to 7:

The development of the geometry begins with two-dimensional objects,applies rotation operators or stretch operators, and results in arealistic, three-dimensional rendition of the turbine wheel. It ispossible in principle to use four-sided surfaces to describe atwo-dimensional rendition of the rotor component. Two methods are usedto parameterize the contours of these four-sided surfaces. The aim ofthis parameterization is to obtain a great variety of shapes while usingas few parameters as possible.

Reference points or reference curves are used as input variables in bothmethods. The input variables are used as output geometries or finalgeometries and/or to position and orientate the primitive objects. Theseinput variables are used in order to increase the accuracy when twoobjects are connected along a common curve. The differences between thetwo methods reside in the way in which the contours are produced. Onetype of primitive objects develops the contour by producing the contourcurve directly (FIG. 4A). The second type produces the contour bydefining a skeleton together with specification of a thicknessdistribution for developing the contour curve (FIG. 4B).

The feature-based geometrical model of a turbine wheel is applied to anintegrally produced rotor stage of a high pressure compressor. Thegeometry firstly has a fictional contour and is not yet analysed oroptimized.

A possible decomposition of a turbine wheel is illustrated in FIG. 5.The bold points mean that these basic objects are optional and includezero or more objects. The basic objects are blades, trunk and shaft.Each basic comprises one or more primitive objects of which differenttypes can be present, and which can be exchanged without changing thestructure of the design. For example, the flange is a basic object whichcan have various topologies such as, for example, a flange for weldingor for assembly. If the type of this basic object is modified, this doesnot change the structure of the rotor disc, but only the topology.

The geometry of the rotor disc is illustrated in FIG. 6 in variousdegrees of detail. The primitive objects are quadrangular objects whichare connected in order to produce the contour depicted. The primitiveobjects illustrated in FIG. 4A are used for all the objects whichillustrate the trunk and the flanges. The blades are produced using atype in accordance with FIG. 4B, the contours being described by askeleton with a thickness distribution.

In general, optimization can begin with specific parts or with thecomplete geometry. This can be performed by considering only thoseparameter sets which influence these parts, or by considering all theparameters. Likewise, it is possible to carry out optimization using thedifferent degrees of detail or assembly. For a primitive object, thisdegree can be modified with regard to a specific part of the geometry bymodifying the details of the primitive objects or by modifying thedegree of assembly of the basic object. Automatic rastering can becarried out on each stage, and analysis can be started.

The advantages of the assembly of the geometry and retaining the maincharacteristics of the primitive objects through the introduction ofconnecting elements are that a consistent raster can be maintainedduring the optimization and the change in the degree of detail orassembly.

The finite element raster produced for a rotor disc is illustrated inFIG. 7. The raster remains substantially unmodified when the degree ofdetail or the position of primitive objects is modified, since thesechanges do not influence the main structure of the assembled geometry.When more objects are added and the degree of assembly rises, thepreceding topology is changed to a minimum extent, and the precedingnetwork can remain substantially unmodified. This may be seen at thetransition between the (connecting) arms and the trunk. The maincharacteristics of the trunk are retained when two (connecting) arms arepresent or are added.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe constructed to include everything within the scope of the appendedclaims and equivalents thereof.

1. A method for modifying, in particular for optimizing, the design of acomponent with regard to one or more criteria using a virtual model ofthe component, said method comprising the steps of: a) producing avirtual model of the component by combining the component from basicobjects with the aid of Boolean operators, b) assigning each basicobject is assigned an information element in which attributes of thebasic object are stored, said attributes including parameter values,interval limits and rules, are stored, c) constructing each basic objectfrom primitive objects which are combined with aid of Boolean operators,the primitive objects being surfaces or bodies which can be decomposedinto rasters, d) assigning each geometrical contact surface or contactline, produced in the case of the Boolean operation between two or moreobjects, a connecting element in which information for coordinating theobjects is stored, e) rastering of the primitive objects by aconventional gridding method, f) modifying a geometrical shape ofindividual or a group of objects is undertaken, wherein the informationof the information elements define the limits of possible modifications.2. Method according to claim 1, wherein the basic objects areconstructed from one or more further basic objects which are combined byBoolean operators, and which are assigned in each case an informationelement in which attributes of the basic object, in particular parametervalues, interval limits and rules, are stored, and each geometricalcontact surface or contact line which is produced in the case of theBoolean operation between two or more objects being assigned aconnecting element in which information for coordinating the objects isstored.
 3. Method according to claim 1, wherein the primitive objectsare constructed from one or more further primitive objects which arecombined by Boolean operators, and which are assigned in each case aninformation element in which attributes of the primitive object, inparticular parameter values, interval limits and rules, are stored, andeach geometrical contact surface or contact line which is produced inthe case of the Boolean operation between two or more objects beingassigned a connecting element in which information for coordinating theobjects is stored.
 4. Method according to claim 3, wherein the basicobjects or primitive objects are assembled with the aid of Booleanoperators from lower geometrical objects which are produced by rotation,stitching or stretching.
 5. Method according to claim 1, wherein onlythe geometrical shape of individual or a plurality of primitive objectsis modified.
 6. Method according to claim 1, wherein the primitiveobjects are standardized rasterable objects such as triangles,rectangles, pentagons, tetrahedra, pentahedra or hexahedra.
 7. Methodaccording to claim 1, wherein the basic objects are, in particular,surfaces, cuboids or rotationally symmetrical bodies.
 8. Methodaccording to claim 1, wherein each primitive object is assigned aninformation element in which attributes of the primitive object, inparticular parameter values, interval limits and rules, are stored. 9.Method according to claim 1, wherein before the rastering of theprimitive objects (step e), the objects are allocated coordinationelements as additional knowledge.